Transponder system

ABSTRACT

A transponder system comprising an interrogating source of HF electromagnetic radiation, and a plurality of transponders which each include a token reader unit to receive a removable token, e.g., a smart card, including onboard data processing capability. The transponders, or a group of transponders, are each arranged when interrogated to transmit a unique HF response modulated by information taken upon the token.

BACKGROUND OF THE INVENTION

The invention relates to a transponder system for monitoring thelocations of objects over relatively large distances.

It is an object of the invention to provide such a system which can bemade available at relatively low cost and which is arranged so that eachtransponder can, in response to the receipt of an interrogating signal,transmit to a monitoring station a response peculiar to thattransponder, or a group of transponders, and which response can beeasily altered to take account of changing circumstances.

BRIEF SUMMARY OF THE INVENTION

It is envisaged that a particularly advantageous application ofinvention might be to the monitoring of licenced fishing vessels, or tothe monitoring of arms equipment, e.g. missiles and tanks.

WO/89/05460, for example, discloses a transponder system comprising aninterrogating source of H.F. electromagnetic radiation and a pluralityof transponders. The present invention is characterized in that eachtransponder includes a token reader unit to receive a removable tokenincluding on board data processing capability, the transponders, or agroup of transponders, each being arranged when interrogated to transmita unique H.F. response modulated by information carried upon the token.

Because of the H.F. signals used, typically between 4 and 28 MHz, thesystem is operative over large distances, say up to 3500 Km. Because ofthe token reader unit and the nature of the token, the transpondersthemselves can be made at relatively low cost and the informationcarried upon the token can be easily changed.

In the case of the fishing vessel application mentioned above, eachvessel licenced under the scheme would be required to have atransponder. A token, e.g. a smart card, would be bought as a licence bythe vessels operator and, in addition to the information identifying theparticular vessel, could also have other information such as whether thetoken has expired encoded onto the token and that informationadditionally could be used to modulate the response.

The token may be replaced when updating is required, but preferably thetoken reader unit includes token writing means and the interrogatingsource is operative to transmit information to be written onto thetoken. In this way updating can be accomplished remotely.

One disadvantage of an H.F. radar system is its poor positionalresolution, which means that it can be difficult to locate an identifiedobject with any greater accuracy than about 10 Km or so.

Preferably each transponder is operatively connected to navigationalsatellite receiving means and is arranged when interrogated to transmitinformation indicative of the position of the transponder.

In this way, the monitoring station can be provided with information onthe precise location of a vehicle so equipped even if its locationcannot be accurately found using a reflected radar signal.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be well understood, embodiments thereofwill now be described with reference to the diagrammatic drawings, inwhich:

FIG. 1 shows a diagrammatic representation of a transponder system;

FIG. 2 shows a schemmatic view of a transponder unit for use in thesystem FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

It will be appreciated that the transponder systems of the presentinvention are broadly applicable to cases where it is designed tocontinuously monitor and communicate automatically with one or more of alarge number of mobile locations.

As previously discussed, one particular application for the invention isfor a fishing vessel monitoring system. Fishing vessels often operate inlarge numbers over a very large area of sea, making monitoringdifficult. In certain cases, where licencing schemes are operating, itis often difficult to locate or enforce licences, but the presentinvention is intended to overcome this problem.

In FIG. 1 an interrogating and, optionally, monitoring station IS may beship or shore mounted and arranged to transmit an H.F. radarinterrogating signal. Each fishing vessel FV includes a transponder Thaving a token reader unit and a token, e.g. a smart card, containing aunique code, as will be described in greater detail later on. Eachtransponder T is also operatively connected to a navigational satellitereceiver GPSR for receiving positional information from the GPS (GlobalPositioning System) satellite system operated by the US government. Theterm "GPS" is intended to encompass any satellite based navigationalsystem.

FIG. 2 shows schematically an HF radar transmitting transponder unit. Anantenna Ant is operatively connected to the unit and typically may be 3meters long. A switch SW, which may be electronic, switches the unitbetween a receive mode RX and a transmit mode TX. The unit includesamplifiers AMD, a frequency source FS, which may run at any suitableH.F. radar frequency depending on the range required. For the fisheriesapplication previously mentioned, this may be between 4 and 8 MHz givinga range of up to 150 Km. Lower frequencies may be appropriate for longerranges. Preferably the frequency is selected according to operationalrequirements, e.g. weather, sea state, size of vessel etc, and thetransponder is arranged to respond to a range of signals. Amodulator/demodulator MDM is present for decoding and coding messageinformation from and onto the received and transmitted signalsrespectively. A delay unit DLY is also present. The transponder may bearranged to transmit only in response to the receipt of an interrogatingsignal intended for that particular unit. For example, the interrogatingsignal may include an identifying code to be compared with a codeprovided within the unit, e.g. held in coding means CDM, or on the tokenitself. A token reader and preferably also writer unit TRW is providedfor reading and writing information from and onto a smart card, or othertoken having on board data processing capability. The smart card isconveniently a contactless smart card, e.g. of the type made by GEC CardTechnology Limited of Walsall England, and which communicates with itsreader/writer unit by inductive coupling. Such systems are robust andcan be installed sealed in fishing vessels without problems of corrosionor damage in use. The coding means CDM is preferably provided both forchecking, if appropriate, that a received identifying code is thecorrect code for that transponder unit to respond to and for checking,if appropriate, that the card is the correct card for that transponderto prevent unauthorised transfer of the card. The transponder unit ispreferably operative to transmit an invalid response if the token isinvalid for that transponder or is absent. The card can be issued, forthe fisheries application mentioned above, on payment of the licencefee. In a preferred embodiment the transponder is arranged to writeinformation onto the card in response to the receipt of an appropriatesignal from the interrogating source. In such a case, when the life ofthe card has expired, but a new licence fee has been paid, the card canbe updated remotely without the need for a new card to be issued. Inaddition to providing a code identifying each respective transponder,the information on the card can provide an indication of whether thecard has expired. Information from the GPS received by the GPS receiverGPSR, indicative of the location of the transponder can also be encodedinto the response so that the monitoring station knows precisely thelocation of the transponder. Such information could be processed withinthe transponder unit and, for example, compared with territoriallimitations, or boundaries, encoded onto the card to check that thevessel has not strayed too far. As previously discussed, conventionalH.F. radar has poor resolution and the implementation of such a systemwill enable a monitoring station to precisely locate vessels soequipped, even at great over-the-horizon distances.

One transponder which might be useful in constructing such a system isdescribed in IEEE J. Oc Eng. Vol OE-6, No. 1 January 1981.

The transponder unit may be provided with further data input means forconnection to a sensor or the like providing data to be transmitted tothe monitoring station, and data output means, such as a display and/oractuator, for displaying data received or performing actions under thedirection of the interrogating signal.

Where a number of transponders are interrogated, a time or frequencyslot arrangement may be utilised, each transponder only transmitting fora given time in a predetermined slot or frequency.

An alternative use of the transponder system could be in monitoring themovement of aircraft over long distances. In particular the monitoringof aircraft over flying a region can be achieved as coding cards wouldonly be issued by a given authority and hence unauthorised over flyingcan be detected and an authorised aircraft can be identified.Information about the aircrafts' route could be stored upon the tokenand relayed to the monitoring station. Similarly such transponder unitscould be fixed to items of arms equipment e.g. tanks and the like, andcards issued by the appropriate arms treaty invigilators.

I claim:
 1. A transponder system comprising an interrogating source ofH.F. electromagnetic radiation, and a plurality of transponders, whereineach includes a token reader unit to receive a removable token includingon board data processing capability, the transponders, or a group oftransponders, each being arranged when interrogated to transmit a uniqueH.F. response modulated by information carried upon the token.
 2. Atransponder system according to claim 1, wherein the token is a smartcard.
 3. A transponder system according to claim 1, wherein eachtransponder is operatively connected to a navigational satellitereceiving means and is arranged when interrogated to transmitinformation indicative of the position of the transponder.
 4. Atransponder system according to claim 1, wherein the token reader unitadditionally includes token writing means and in which the interrogatingsource is operative to transmit information to be written onto thetoken.
 5. A transponder system according to claim 1, wherein eachtransponder is located upon a fishing vessel or other vehicle and inwhich the tokens comprise licences having a limited life.
 6. Atransponder system comprising an interrogating source of H.F.electromagnetic radiation and a plurality of transponders, eachtransponder including a token reader unit in communication with aremovable token including on board data processing capability, saidreader unit and token being in communication without physical contact,said transponders or a group thereof each being arranged wheninterrogated to transmit a unique H.F. response modulated by informationcarried upon its respective token.
 7. The transponder system of claim 6further comprising said interrogating source being operative to transmita unique identifying code to each of said transponders whereupon saidtransponder transmits its said unique H.F. response.
 8. The transpondersystem of claim 6 said information carried upon each token includes acode and each token reader unit in each transponder including acomparable reader code which it compares to said token code to determinewhether the token is valid for that transponder.
 9. The transpondersystem of claim 8 wherein said unique transmitted response is an invalidresponse when said reader unit code comparison indicates said token isinvalid for said transponder or absent.